A Modelling Framework for Lightning-Induced Common-Mode Currents in Photovoltaic Modules and Small Arrays

Lightning generates electromagnetic interference (EMI) that can couple into photovoltaic (PV) installations and induce transient phenomena capable of damaging system components. Existing research primarily focuses on coupling through internal conductive paths, whereas studies on leakage currents do examine cell-to-frame effects but largely neglect the internal cell layout and cell impedance. Consequently, the influence of cell-to-frame coupling under lightning conditions remains insufficiently characterised. This dissertation aims to develop and validate computational electromagnetic (CEM) modelling techniques to replicate cell-to-frame coupling in PV installations and to evaluate the magnitude and significance of lightning-induced common-mode (CM) currents. A range of PV modules, spanning small-scale to full-size units and a complete PV array, were measured using a vector network analyser (VNA) at lightning-relevant frequencies to quantify cell-to-frame coupling. The CEM-based simulations showed strong agreement with the measurements, within 3–5 dB across the full frequency range, without the need for iterative parameter tuning. Compared to conventional parasitic capacitance models, the proposed methodology demonstrated improved low-frequency accuracy while inherently incorporating the higher-frequency characteristics typically omitted in existing approaches. For smaller modules, the geometric fidelity of the cell layout proved critical. Simplifying the cells to a wire-equivalent structure resulted in deviations exceeding 20 dB relative to the measured responses. For larger modules, the results indicated that an accurate geometric representation of the cells sufficiently captures the cell inductance and resistance when appropriate material modelling is applied. This enables improved high-frequency replication and establishes an efficient, scalable modelling technique that yields accuracy improvements of 2–10 dB over established methods. The methodology was further validated using five modules mounted on a single-axis tracker, where measurements and simulations agreed within 3–5 dB across the 50 MHz band. Additionally, a novel wideband model for a surge protection device (SPD) was developed by incorporating previously neglected resistive elements, improving its representation in both the frequency and time domains. Time-domain simulations incorporating the adapted SPD model and a simplified earthing system revealed that worst-case lightning scenarios can induce transient currents exceeding 490 A in the PV structure. Even when applying the prescriptions of the International Electrotechnical Commission (IEC) 62305 lightning protection standard, currents greater than 80 A may still occur. Frequency-domain analysis of the coupled currents identified significant coupling between the module frame and the cells in the 2 MHz band, consistent with the experimental observations. The proposed modelling methodology enables the accurate evaluation of lightning-related transient coupling for both direct and indirect lightning flashes. Furthermore, the results demonstrate that conventional parasitic capacitance modelling approaches have limited applicability to lightning-related studies, and that accurate geometric modelling of the PV module is essential for capturing high-frequency behaviour in PV installations.

Grantor dc:publisher

Stellenbosch : Stellenbosch University

Year dc:date.issued

2026

Author dc:creator

• Smit, Herme Charles

Advisors dc:contributor.advisor

• Rix, Arnold Johan
• Coetzer, Kurt Michael

Language dc:language.iso

en

Repository record dc:identifier.uri

https://scholar.sun.ac.za/handle/10019.1/135820

OAI identifier oai:identifier

oai:scholar.sun.ac.za:10019.1/135820